The current study explored the association between a large-scale federally funded preschool intervention and the social and emotional development of participants. Data were drawn from the Chicago Longitudinal Study (CLS) and included 1,378 primarily African American youth who participated in the CLS and had scores for two or more identifiable social and emotional competency indicators from age 7 through age 15. Findings suggest that program participation was associated with both shorter- and longer-term social and emotional outcomes. The effect sizes for the longer term were modest, and several remained above the level considered practically significant (0.20). The strongest short-term effect was seen for social adjustment in school at ages 7 and 89 with d's of 0.45 and 0.33, respectively. These include social adjustment in school (d = 0.34), assertive social skills (d = 0.21), task orientation (d = 0.21), frustration tolerance (d = 0.22), and peer social skills (d = 0.24).